Semiconductor devices are manufactured by repeating a photolithographic technique in which exposure light is applied to a mask (transfer mask) such as a photomask with a circuit pattern drawn thereon and the circuit pattern formed on the mask is transferred onto a semiconductor substrate (semiconductor wafer) through a demagnification optical system. The transfer mask is produced by forming the circuit pattern in a substrate (mask blank) formed with an optical thin film. Such an optical thin film is generally a thin film composed mainly of a transition metal compound or a thin film composed mainly of a transition metal-containing silicon compound. As the optical thin film, a film functioning as a light-shielding film or a film functioning as a phase shift film is selected according to the purpose.
The transfer mask such as photomask is for use as an original form for manufacturing semiconductor devices having minute patterns, and is demanded to be defect-free. This naturally leads to that the mask blank is also demanded to be free of defects. In addition, at the time of forming a circuit pattern, a resist film for processing is formed on a mask blank formed thereon with an optical thin film, and a final pattern is formed through an ordinary lithography step such as an electron beam lithography. Therefore, the resist film is also demanded to be free of defects such as pinholes. Under such circumstances, many investigations have been made as to the defect detecting technique for transfer masks and mask blanks.
JP-A 2001-174415 (hereinafter referred to as Patent Document 1) and JP-A 2002-333313 (hereinafter referred to as Patent Document 2) describe a method of applying laser light to a substrate to detect a defect and/or a foreign matter from scattered light, particularly a technology in which asymmetry is imparted to detection signals to determine whether a defect in question is a bump defect or a pit defect. In addition, JP-A 2005-265736 (hereinafter referred to as Patent Document 3) describes a technology in which deep ultraviolet (DUV) light conventionally used for general optical mask pattern inspection is used as inspection light. Further, JP-A 2013-19766 (hereinafter referred to as Patent Document 4) describes a technology in which inspection light is used for scanning in the state of being divided into a plurality of spots and reflected beams are received individually by light detection elements. On the other hand, JP-A 2007-219130 (hereinafter referred to as Patent Document 5) discloses a technology in which extreme ultraviolet (EUV) light having a wavelength of around 13.5 nm is used as inspection light to distinguish whether a defect in an EUV mask blank is a pit defect or a bump defect.